1. Field of the Invention
The present invention relates to a multiway valve for use with a hydraulic or pneumatic device. More specifically, the invention relates to a multiway valve which can be operated by a servo valve, and which may be utilized to operate a fluid device in both a resting and an activated mode.
2. Description of the Prior Art
Multiway slide valves are well known in the art for the operation of fluid based machinery. One such valve is disclosed in U.S. Pat. No. 4,491,155, issued Jan. 1, 1985, which is hereby incorporated into this specification by reference. This valve utilizes a sliding valve body having a recessed land at its center. Three ports with associated fluid chambers are disposed along a central bore, in which the valve body is slidably located. Sealing rings separate each of the chambers. In operation, the valve body is moved such that the recessed land is displaced from a central position toward one of the two extreme positions. This allows fluid communication across the land between the center fluid chamber and one of the end fluid chambers.
Servo operated valves are also well known. U.S. Pat. No. 4,627,597, issued Dec. 9, 1986, discloses a balanced servo valve with optional manual activation for mounting on a multiway valve. The specification of U.S. Pat. No. 4,627,597 is also hereby incorporated into this specification by reference. The servo valve has an inlet and an outlet port which are separated by a valve body. The valve body is held in the closed position, relative to the inlet and outlet ports, by a spring. The valve body is surrounded by a coil, which when activated moves the valve body against the spring and allows fluid communication between the inlet and the outlet ports.
A servo-operated, multiway valve has also been developed, and is illustrated in various catalogs of WABCO Westinghouse Fahrzeugbremsen GmbH, including Steuerungstechnik, Gerat 572, October 1976. This device utilizes the servo valve to displace the sliding valve body of the multiway valve. The first, or inlet chamber introduces fluid to the multiway valve. The second, or outlet chamber is connected to a fluid-operated device, and allows the fluid to pass to the device. The third, or vent chamber serves as a return to tank or as a vent to the atmosphere.
The servo valve is connected to the multiway valve through two passages. The first is continuously connected with the inlet chamber of the multiway valve and allows fluid to pass to the servo valve. The second leads from the servo to a control chamber within the multiway valve. The control chamber, when charged with fluid, displaces the multiway valve body from its resting position. The fluid flow from the servo to the control chamber is blocked by the servo valve body in the resting position.
When the servo valve is activated, it allows fluid to flow from the first servo passage into the second servo passage, and from there into the multiway valve. This pressurizes the control chamber in the multiway valve. The fluid introduced into the control chamber displaces the multiway valve body, such that the inlet chamber is closed off from the outlet chamber which feeds the consumer device. The outlet chamber is then connected with the vent chamber, which serves as a pressure exit chamber. In such a design and switching mode, the multiway valve has the function of a fluid-escape valve, as the fluid consuming device is in communication with the fluid source when the valve is at rest.
If such a multiway valve is to be used as a ventilating valve, structural modifications must be made to the multiway valve. In such an embodiment, the fluid actuated device is not in communication with the fluid source in the resting position. The chambers are reversed in order along the valve body, so that the former vent chamber, which was closed off from the outlet chamber at rest, becomes the inlet chamber. In a like manner, the former inlet chamber, which was in communication with the outlet chamber at rest, becomes the vent chamber. At rest, fluid is introduced to the inlet chamber, and the outlet chamber and vent chambers are in communication with the atmosphere or a fluid return.
When the servo is activated, the multiway valve body is displaced, so that the inlet chamber is in communication with the outlet chamber, and fluid flows to the consuming device. In order for such an embodiment to operate properly, the multiway valve must be modified structurally from its first embodiment. A passage must be made between the vent chamber of the first embodiment, which becomes the inlet chamber of the second embodiment, and the servo. This is to provide a continuous source of fluid to the servo. Additionally, the inlet chamber of the first embodiment, which has become the vent chamber in the second embodiment, may not have any connection to the servo chamber.
If one wishes to construct a pressure medium-actuatable device so that ventilation or pressurization of this device are both optionally possible when the servo valve is actuated, it is necessary to employ two servo-operated multiway valves. One of each of the above described embodiments must be utilized. As stated, these multiway valves differ in that the first chamber in the case of one multiway valve and the third chamber in the case of the second multiway valve must have a continuous connection to the entrance chamber of the assigned servo valve. It is thus necessary to provide a separate servo-operated multiway valve for each application purpose.
What is lacking in the art, therefore, is a single valve which can be utilized optionally to operate a fluid device in both its resting and activated modes, without modification.